l-cysteine intercalated layered double hydroxide for highly efficient capture of U(VI) from aqueous solutions

Ion-imprinted macroporous polyethyleneimine incorporated chitosan/layered hydrotalcite foams for the selective biosorption of U(VI) ions

In order to prevent uranium pollution and recovery uranium resources, it was necessary to find a highly efficient adsorbent for radioactive wastewater treatment. Herein, U(VI) imprinted polyethyleneimine (PEI) incorporated chitosan/layered hydrotalcite composite foam (IPCL) was synthesized by combining ion-imprinting and freeze-drying techniques. IPCL has a high amino/imino content and an ultralight macroporous structure, making it capable of efficiently adsorbing U(VI) and easy to separate; Especially after ion-imprinting, vacancies matching the size of uranyl ions were formed, significantly improving U(VI) selectivity. The adsorption isotherms and adsorption kinetics were in accordance with the Freundlich model and PSO model respectively, indicating that heterogeneous adsorption of U(VI) by the adsorbents. The adsorption capacity of IPCL-2 for U(VI) reached 278.8. mg/g (under the conditions of optimal pH 5.0, temperature of 298 K, contact time of 2 h, and adsorbent dosage of 0.2 g/L), which is almost double of that for the non-imprinted foam (PCL-2, 138.2 mg/g), indicating that IPCL-2 can intelligently recognize U(VI). The heterogeneous adsorption mechanism of U(VI) by IPCL-2 involves complexation, ion-exchange and isomorphic substitution. The adsorption of U(VI) by IPCL-2 is spontaneous and endothermic. IPCL-2 has excellent adsorption performance for U(VI), and is a promising adsorbent for radioactive pollution control.

Facile preparation of high-efficiency peroxidase mimics: modulation of the catalytic microenvironment of LDH nanozymes through defect engineering induced by amino acid intercalation

Nanozymes have gained much attention as a replacement for natural enzymes duo to their unique advantages. Two-dimensional layered double hydroxide (LDH) nanomaterials with high physicochemical plasticity are emerging as the main forces for the construction of nanozymes. Unfortunately, high-performance LDH nanozymes are still scarce. Recently, defects in nanomaterials have been verified to play a significant role in modulating the catalytic microenvironment, thereby improving catalytic performances of nanozymes. Therefore, the marriage between defect engineering and LDH nanozymes is expected to spark new possibilities. In this work, twenty kinds of natural amino acids were separately inserted into the interlayer of CoFe-LDH to obtain defect-rich CoFe-LDH nanozymes. The peroxidase (POD)-like activity and catalytic mechanism of the as-prepared LDH nanozymes were systematically studied. The results showed that the intercalation of amino acids can effectively enhance the POD-like activity of LDH nanozymes owing to the increasing oxygen/metal vacancies. And l-cysteine intercalated LDH exhibited the highest catalytic activity ascribed to its thiol group. As a proof of concept, LDH nanozymes with superb POD-like activity were used in biosensing and antibacterial applications. This work suggests that modulating the catalytic microenvironment through defect engineering is an effective way to obtain high-efficiency POD mimics.

Enhancing the effectiveness of Alkaline Phosphatase and bone matrix proteins by tunable metal-organic composite for accelerated mineralization

The irregular expression of bone matrix proteins occurring during the mineralization of bone regeneration results in various deformities which poses a major concern of orthopedic reconstruction. The limitations of the existing reconstruction practice paved a way for the development of a metal-organic composite [TQ-Sr-Fe] with Metal ions strontium [Sr] and iron [Fe] and a biomolecule Thymoquinone [TQ] in an attempt to enhance the bone mineralization due to their positive significance in osteoblast differentiation, proliferation and maturation. TQ-Sr-Fe was synthesized by in-situ coprecipitation and subjected to various characterization to determine their nature, compatibility and osteogenic efficiency. The crystallographic and electron microscopy analysis reveals sheet like structure of the composite. The negative cytotoxicity of TQ-Sr-Fe in the MG 63 cell line signified their biocompatibility. Cell adhesion and proliferation rate affirmed osteoconductive and osteoinductive nature of the composites and it was further supported by the gene expression of osteoblastic differentiation. The sequential expression of bone matrix proteins such as OCN, SPARC, COL 1, and Alkaline Phosphatase elevate the calcium deposition of MG-63 osteoblast like cells and initiates mineralization compared to control. Thus, the metal-organic composite TQ-Sr-Fe would make a suitable composite for accelerating mineralization process which would leads to faster bone regeneration.

Layered double hydroxide intercalated with dimethylglyoxime for highly selective and ultrafast uptake of uranium from seawater

In this study, we demonstrate the first example of a MgAl layered double hydroxide intercalated by a ketoxime compound (dimethylglyoxime, DMG), that is, MgAl-DMG-LDH (abbr. DMG-LDH), which exhibits excellent capture of uranium (U(VI)) both at high (ppm) and low (ppb) concentrations. The as-formed DMG-LDH shows an enormous maximum U(VI) sorption capacity (qUm) of 380 mg g^-1 and an exceptionally rapid sorption rate (k₂ = 2.97 g mg^-1 min^-1), reaching a high uptake of 99.14% within 5 min. For natural and contaminated seawater with high concentrations of Na⁺, Ca²⁺, Mg²⁺ and K⁺ concomitant cations, the DMG-LDH still can trap ∼85% U, displaying highly effective sorption toward U. The interaction mechanism between UO₂²⁺ and DMG^2- provides an important reference for the development of highly effective capture of U(VI) by ketoxime materials. The DMG-LDH is currently the best ketoxime material for uranium extraction from nuclear waste and seawater.

A critical review of uranium contamination in groundwater: Treatment and sludge disposal

Dissolved uranium in groundwater at high concentrations is an emerging global threat to human and ecological health due to its radioactivity and chemical toxicity. Uranium can enter groundwater by geochemical reactions, natural deposition from minerals, mining, uranium ore processing, and spent fuel disposal. Although much progress has been made in uranium remediation in recent years, most published reviews on uranium treatment have focused on specific methods, particularly adsorption. This article systematically reviews the major treatment technologies, explains their mechanism and progress of uranium removal, and compares their performance under various environmental conditions. Of all treatment methods, adsorption has received much attention due to its ease of use and adaptability under various conditions. However, salinity and competition from other ions limit its application in actual field conditions. Biosorption and bioremediation are also promising methods due to their low-cost and chemical-free operation. Strong base anion exchange resins are more effective at typical groundwater pH conditions. Advanced oxidation processes like photocatalysis produce less sludge and are effective even at low uranium concentrations. Electrocoagulation shows significantly improved performance when organic ligands are added prior to treatment. The significant advantages of membrane filtration are high removal efficiency and the ability to recover uranium. While each technology has its merits and demerits, no single technology is entirely suitable under all conditions. One major area of concern with all technologies is the need to dispose of liquid and solid waste generated after treatment safely. Future research must focus on developing hybrid and state-of-the-art technologies for effective and sustainable uranium removal from groundwater. Developing holistic management strategies for uranium removal will hinge on understanding its speciation, mechanisms of fate and transport, and socio-economic conditions of the affected areas.

Confinement effect of layered double hydroxide on intercalated pyromellitic acidic anions and highly selective uranium extraction from simulated seawater

The oxygen-rich pyromellitic acidic anions (PMA4-) have been intercalated into MgAl-layered double hydroxide to fabricate the MgAl-PMA-LDH (abbr. PMA-LDH) composite, exhibiting excellent adsorption performance toward uranium (U(VI)). Benefiting from the...

High-efficient removal of U(VI) from aqueous solution by self-assembly pomelo peel/palygorskite composite

The efficient separation of low-concentration radionuclides by the eco-friendly adsorbent is a compelling requirement in the development of nuclear industry. Hence, a novel composite consisted of one-dimensional palygorskite (Pal) and three-dimensional pomelo peel (PP) is prepared by self-assembly approach (PP/Pal) and coupling agent approach (PP/KPal) for removing uranium (U(VI)) from aqueous solution. Moreover, the mass ratio (PP/Pal), adsorbent dosage, pH, contact time, temperature, and ionic strength are investigated. Two adsorption kinetic models and isotherm models are used to investigate the kinetic behaviors and adsorption capacity, respectively. The maximum adsorption capacities were 370.5 mg·g^-1 on PP/Pal and 357.3 mg·g^-1 on PP/KPal at pH 6.0, contact time 150 min and 25 °C. Meanwhile, the composite can be easily separated from water via a simple filtering. Furthermore, thermodynamic parameters indicate that adsorption is an endothermic and spontaneous process. And the surface complexation, ion exchange, and electrostatic attraction play a vital role. This work shows that the PP/Pal composite with high efficiency, low cost, and green has a further application in the treatment of wastewater containing U(VI).

Recent innovations in functionalized layered double hydroxides: Fabrication, characterization, and industrial applications

Layered Double Hydroxides (LDHs) are a group of hydrotalcite-like nano-sized materials with cationic layers and exchangeable interlayer anions. The wide range of divalent and trivalent cationic metals and anionic compounds are employed in the synthesis of LDH materials, which have improved their importance among the researchers. Because of their high anion exchange property, memory effect, tunable behavior, bio-friendly, simple preparation, and their affordability, these nano-materials are essentially interested today. Modification of LDHs improves their behaviours to make them appropriate in industrial fields, including biological, adsorbent, mechanical, optical, thermal, electrical fields, etc. This review has critically discussed the structural features, main properties, and also clarified the most important methods of modification and intercalation of LDH nano-materials. Moreover, some novel reported researches related to the successful modification of LDH materials have been characterized and briefly the advantages, disadvantages, and applications are presented in the industrial fields.

Investigation of a modified metal-organic framework UiO-66 with nanoscale zero-valent iron for removal of uranium (VI) from aqueous solution

A novel composite material (nZVI/UiO-66) of nanoscale zero-valent iron (nZVI) with a functionalized metal-organic framework was synthesized by this study via a coprecipitation method, which was used for the efficient removal of U(VI) in the aqueous solution. The nZVI/UiO-66 had an excellent removal capacity of 404.86 mg g^-1 with an initial U(VI) concentration of 80 mg L^-1, 313 K and pH = 6. The transmission electron microscopy (TEM) revealed that nZVI particles were inhomogeneously distributed on the surface of UiO-66. The analysis by the X-ray diffraction (XRD) has further illustrated that the introduction of nZVI did not change the structure of UiO-66. The adsorption process closely followed the pseudo-second-order kinetic and the Freundlich isotherm model. The removal process of U(VI) by nZVI/UiO-66 was spontaneous and endothermic. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses have illustrated that the mechanism was mainly related to adsorption of U(VI) from UiO-66 and reduction of U(VI) by nZVI. The Zr-O bonds were shown to play a vital role in the uranium removal. nZVI/UiO-66 could be recycled. The uptake rate could be maintained at around 80% after 5 cycles of use. Therefore, these results manifested that the nZVI/UiO-66 is a promising sorbent for the efficient and selective removal of U(VI) in radioactive wastewaters.